1. Field of the Invention
The present invention relates to electrical alternator systems employing a flywheel on gasoline engines. More particularly, the present invention relates to a marine engine alternator system constructed in conjunction with a flywheel of a marine engine.
2. Description of the Prior Art
It is known in providing electrical alternators in conjunction with gasoline engines, and particularly outboard marine engines, to employ a flywheel which is typically aluminum die cast, as a rotor of the alternator. Magnets are provided at an inside wall of the flywheel. A stator is mounted within a cup-shaped portion of the flywheel such that end faces of pole legs having coils thereon are located adjacent the magnets on the flywheel. As the flywheel rotates, the magnets move past the stator pole end faces so as to generate electric currents in the associated alternator coils.
One such prior art outboard marine engine flywheel arrangement is shown in FIG. 1. The aluminum die cast flywheel 230 is cup-shaped with a central hub insert 231 which is a separate piece insert molded in a central aperture of the flywheel. Insert 231 receives a drive shaft 231' of the marine engine. Such a flywheel is typically mounted near a top end of the engine within the engine outer casing. Ring gear 232 is mounted on a shoulder 233 around a periphery of the flywheel and abutting against an inset outer surface 234. A starter motor gear (not shown) engages with teeth of the ring gear 232 to turn the motor shaft 231' via the flywheel 230 and thus start the engine.
Within the inner cup-shaped portion 235 of the flywheel, an annular steel ring 236 is received within a pocket 229 having an inner wall 229'. The steel ring is insert molded there to increase the inertia of the flywheel since steel is approximately three times the weight of aluminum, of which the remainder of the flywheel is constructed.
Against an inner wall 238 of the annular ring 236, a plurality of magnets 237 are mounted in a circular pattern. For example, twelve such magnets may be provided, each of which is either a north or a south magnet, and each of which may complete an arc of approximately 28.degree.. Typically such ceramic magnets have a B.sub.R of approximately 3800 gauss (ceramic magnets). Alternatively, elastomer bonded ferrite composite materials may be provided in strip form around the inner wall 238. The elastomer bonded magnet design typically has a B.sub.R of 1750 gauss. The elastomer magnet is thinner, however, and has a thickness of approximately 0.185 inches compared to 0.356 inches for the ceramic magnets.
The thickness of the peripheral wall 239 adjacent the steel ring 236, and shown at T1, is, for example, 0.6 inches given an outer diameter of D1=8.955 at the recess wall 234 where the ring gear mounts. The steel ring 236 typically can have a wall thickness T2 of 0.350 inches. The inner surface 238 at which the magnets 237 are mounted thus defines the greatest radius at which the magnets can be located. Since the starter motor configuration is given for a given marine engine design, and since typically the ring gear has a given thickness, the thickness T1 of the flywheel wall and the thickness T2 of the steel ring thus determine the maximum radial positioning of each of the magnets from a center axis 228. The total thickness of the wall an steel ring expressed as a percentage of the radius is: ##EQU1##
Additionally, the peripheral wall 239 of the die cast flywheel has a thickness T1 sufficient to retain the steel ring during a so-called "burst testing" wherein the flywheel is rotated at higher and higher RPMs until the flywheel will burst or disintegrate.
Accordingly, in the prior art for a given engine casing dimensioning and starter motor positioning, the magnets 237 have a maximum radial displacement from the center axis 228 defined by the thick wall T1 and thick steel ring having dimension T2. With such a prior art design, the magnets move past the pole faces 240 (shown schematically) at a given velocity for a certain engine cranking RPM.
It is also known in non marine engine applications to provide a stamped steel flywheel as opposed to an aluminum die cast flywheel. However, such stamped steel flywheels are expensive to produce and have multiple pieces due to their stamped construction. Furthermore, such prior art units have relatively thick outer walls such that for given engine dimensions, the ring magnets are still positioned a substantial distance inwardly from the ring gear.
With such prior art flywheels, in order to generate sufficient voltage in coils associated with the alternator such as trigger coils, a substantial RPM is required for starting due to the limited velocity of movement of the magnets past the stator coils due to the limited radial displacement thereof. A pull cord (not shown) has an end attached such as in a slot 240 on an outer flange 241. As is well known, as the rope is pulled, the flywheel is rotated for manual starting of the engine. Also, the starter motor must have a given rating in order to rotate the flywheel at a sufficiently high speed for starting.
It is also known in small engine ignition systems to provide trigger coils which sense passage of the magnets on the flywheel to generate a trigger signal. The trigger signals may be employed to produce ignition pulses, such as by a capacitive discharge ignition circuit controlled by the trigger signals. Exemplary of such systems are U.S. Pat. Nos. 3,741,185 and 3,961,618.
With such prior art systems, the trigger pulses from the pickup or trigger coils are dependent on RPM. At low RPM, slow flux changes result in weak output pulses from the trigger or pickup coils.
It is also known in prior art systems to provide a shunt regulation system connection to alternator coils on the stator of the alternator to regulate a rectified output voltage for battery charging and electrical system operation. Substantial power is lost through heat dissipation with such shunt systems. Alternatively, it is known to also employ a full wave regulating system to regulate voltage to the battery and electrical system of the vehicle. However, at low RPM series connected control devices do not turn on and the battery is not charged.